Resin composition capable of laser marking method, and marked molded article

ABSTRACT

A resin composition capable of laser marking according to the present invention includes a polyolefin resin in combination with a laser-sensitive component such as a carbon black or metallic compound white pigment and a dispersing aid such as a higher fatty acid compound. The polyolefin resin includes, for example, a polypropylene. The resin composition may further include about 0.5 to 30 parts by weight of an elastomer relative to 100 parts by weight of the polyolefin resin. By irradiating an surface of a molded article obtained from the resin composition with a laser, a mark having a sharp and uniform contrast can be formed on the surface of the molded article.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP99/03976 which has an Internationalfiling date of Jul. 26, 1999, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a resin composition where, for example,a character, a symbol, a picture or a photograph can be marked with alaser on a surface of a molded article, to a method for the marking of amolded article obtained from the resin composition, and to a markedmolded article.

BACKGROUND ART

Conventionally, as methods for laser printing on a surface of a moldedarticle composed of a polyolefin resin, a method in which a siliconsubstance is incorporated into the resin as indicted in, for example,Japanese Unexamined Patent Application Publication No. 7-286074, and amethod in which a metal such as aluminium or copper is incorporated intothe resin as disclosed in Japanese Unexamined Patent ApplicationPublication No. 1-224186 are known. However, such a silicon substancehas a poor compatibility with a polyolefin and frequently becomes poorlydispersed. As a result, a sharp printing with a laser cannot besignificantly expected. When

DISCLOSURE OF INVENTION

Accordingly, an object of the present Invention is to provide a resincomposition and marking method which can form a mark having a sharp anduniform contrast on a surface of a molded article with a laser, as wellas a molded article on a surface of which a mark having a sharp anduniform contrast is formed.

Another object of the present invention is to provide a resincomposition and marking method which can laser mark withoutdeterioration in workability and mechanical characteristics, as well asa molded article which is marked without deterioration in workabilityand mechanical characteristics.

After intensive investigations to achieve the above objects, the presentinventors found that when a molded article obtained from a resincomposition including a polyolefin resin in combination with specificcomponents is irradiated with a laser, printing with a sharp and uniformcontrast can be formed on a surface of the molded article. The presentinvention has been accomplished based on these findings.

Specifically, the present invention provides (i) a resin composition forwhite marking, which is capable of laser marking and includes apolyolefin resin in combination with a carbon black having a meanparticle size of 10 to 100 nm and a dispersing aid selected from higherfatty acids and higher fatty acid amides, and is capable of whiteprinting with a laser, and (ii) a resin composition so black marking,which is capable of laser marking, includes a polyolefin resin incombination with a carbon black having a mean particle size of 10 to 100nm, a metallic compound white pigment, and a dispersing aid selectedfrom higher fatty acid compounds, and is capable of black printing witha laser.

In another aspect, the present invention provides a method for whitemarking of a molded article, which includes the step of irradiating asurface of a molded article with a laser to thereby mark the surface inwhite, which molded article is obtained from the resin composition (i)for white marking, and a method for black marking of a molded article,which includes the step of irradiating a surface of a molded articlewith a laser to thereby mark the surface in black, which molded articleUs obtained from the resin composition (ii) for black marking.

In addition and advantageously, the present invention provides a moldedarticle which is composed of the resin composition (i) for white markingand has a surface marked in white with a laser, and a molded articlewhich is composed of the resin composition (ii) for black marking andhas a surface marked in black with a laser.

BEST MODE FOR CARRYING OUT THE INVENTION

A polyolefin resin for use in the present invention may be any ofolefinic homopolymers and copolymers (random copolymers, and blockcopolymers) characteristics.

After intensive investigations to achieve the above objects, the presentinventors found that when a molded article obtained from a resincomposition including a polyolefin resin in combination with specificcomponents is irradiated with a laser, printing with a sharp and uniformcontrast can be formed on a surface of the molded article. The presentinvention has been accomplished based on these findings.

Specifically, the present invention provides a resin composition capableof laser marking, which includes a polyolefin resin in combination witha laser-sensitive component and a dispersing aid.

In another aspect, the present invention provides a method for marking amolded article, which includes the step of irradiating and marking asurface of a molded article with a laser, which molded article isobtained from the resin composition.

Additionally, the present invention provides a molded article which iscomposed of the resin composition and has a surface marked with a laser.

BEST MODE FOR CARRYING OUT THE INVENTION

Polyolefin resins for use in the present invention may be any ofolefinic homopolymers and copolymers (random copolymers, and blockcopolymers), such as polypropylenes, polyethylenes, and other olefinichomopolymers; ethylene-propylene copolymers, and other copolymers eachcontaining propylene as a monomeric component; and ethylene-vinylacetate copolymers and other copolymers each containing ethylene as amonomeric component. Among them, a polypropylene (PP) can be mostadvantageously used, from the viewpoint of, for example, balance inphysical properties, heat resistance, and price. The polypropylenepreferably has a melt flow rate (MFR) of about 0.5 to 50 (g/10 min.) anda flexural modulus of about 10000 to 18000 kgf/cm². If MFR isexcessively low, a usual molding tends to be difficult, in contrast, ifit is excessively high, sufficient mechanical strengths cannot besignificantly obtained. If the flexural modulus is excessively low, theresulting resin becomes too soft and tends to invite creep in use, incontrast, if it is excessively high, the resulting resin becomes toohard and tends to invite cracking in use.

The invented resin composition may further comprise other resins inaddition to the polyolefin resin. For example, the resin composition cancomprise olefinic, styrenic, polyester-based, polyamide-based, and otherelastomers (including natural rubbers, synthetic rubbers, andthermoplastic elastomers) to thereby control elastic modulus, when aresin having a high crystallinity and a high elastic modulus such as apolypropylene or polyethylene is used as the polyolefin resin. Theamount of the elastomer is, for example, about 0.5 to 30 parts byweight, and preferably about 5 to 25 parts by weight relative to 100parts by weight of the polyolefin resin when a polypropylene or the likeis used as the polyolefin resin. If the amount of the elastomer isexcessively small, advantages of the addition of the elastomer cannot beobtained. In contrast, if it is excessively large, the elastic modulusbecomes excessively low to thereby deteriorate dimensional stability ofthe resulting molded article in some cases.

Laser-sensitive components (laser-susceptible components) for use in thepresent invention include, for example, components that physically orchemically change with laser irradiation. Known or conventionallaser-susceptible components which are used in marking with the use of alaser can be used. Such components include, but are not limited to, acarbon black and other black pigments, metallic compound white pigments,and other inorganic pigments. Each of these components can be used aloneor in combination. A mark in a desired color can be formed byappropriately selecting the type of the laser-sensitive component.Generally, the use of a black pigment such as a carbon black can yieldwhite printing, and the use of a white pigment such as a metalliccompound white pigment can yield black printing. In this connection, thecombination use of a white pigment such as a metallic compound pigmentand a black pigment such as a carbon black can yield a very sharp blackmarking.

A variety of carbon black can be used as the carbon black regardless ofmaterials and production methods. Such carbon black includes, but is notlimited to, furnace black, channel black, acetylene black, and ketjenblack. The particle size and oil absorption of the carbon black tend toaffect marking properties. The carbon black preferably has a meanparticle size of about 10 to 100 nm and an oil absorption of about 50 to500 ml/g. If the carbon black has an excessively small mean particlesize or an excessively large oil absorption, particles are too fine andhandling property tends to be deteriorated. If the carbon black has anexcessively large mean particle size or an excessively small oilabsorption, dispersibility is decreased to thereby deteriorate theappearance of the molded article.

The metallic compound white pigment includes, but is not limited to,titanium oxide, lead oxide, zinc oxide, and other metal oxides; talc(magnesium silicate), calcium carbonate, potassium titanate, and othermetal salts (carbonates, silicates, titanates, and other oxo acid saltsof metals). Among them, titanium oxide is particularly advantageouslyused. Each of these metallic compound white pigments can be used aloneor in combination.

The amount of the laser-sensitive component can be appropriatelyselected, depending on the type of the component, within a range ofabout 0.005 to 50% by weight relative to the overall resin composition.For example, when a carbon black is used as the laser-susceptiblecomponent, the amount is about 0.01 to 5% by weight, preferably about0.03 to 4% by weight, and more preferably about 0.05 to 3% by weight,relative to the overall resin composition. When the metallic compoundwhite pigment is used, the amount is about 0.2 to 50% by weight, andpreferably about 0.5 to 40% by weight relative to the overall resincomposition. If the amount of the laser-sensitive component isexcessively small, printing (white printing or black printing) having asharp contrast cannot be significantly obtained. If the amount isexcessively large, dispersibility is decreased, frequently resulting ina decreased resolution in a printed region.

Dispersing aids for use in the present invention are not particularlylimited as far as they can improve dispersibility of thelaser-susceptible component. Preferably, fatty acid compounds are used.Such fatty acid compounds include saturated or unsaturated fatty acidshaving two or more carbon atoms (e.g., about 2 to 32 carbon atoms) orderivatives (e.g., salts, esters, and amides) of these fatty acids.Preferred fatty acid compounds include, but are not limited to, lauricacid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleicacid, linolenic acid, and other higher fatty acids (e.g., fatty acidseach having about 10 to 20 carbon atoms); zinc laurate, calciumstearate, zinc stearate, sodium oleate, and other salts (e.g., alkalimetal salts, alkaline earth metal salts, and zinc salts) of the higherfatty acids; ethylenebisstearamide, lauramide, and other amides of thehigher fatty acids; and other higher fatty acid compounds (higher fattyacids or derivatives thereof).

The amount of the dispersing aid is, for example, about 0.005 to 6% byweight, and preferably about 0.01 to 5% by weight relative to theoverall resin composition. If the amount of the dispersing aid isexcessively small, dispersibility of the laser-sensitive component islow, and a sharp printing cannot significantly obtained. If the amountof the dispersing aid is excessively large, there may be a problem suchthat the dispersing aid evaporates or sublimes in molding process andadheres to a mold (die).

Methods for preparing the resin composition capable of laser marking inthe present invention include (1) a method in which predeterminedamounts of the polyolefin resin, laser-sensitive component, dispersingaid, and where necessary other resins (e.g., an elastomer) and additivesare mixed, and the resulting mixture is kneaded and is pelletized by aconventional melting kneading process. Alternatively, (2) thelaser-sensitive compound, dispersing aid, and the like are mixed toyield a master batch, and a predetermined amount of the master batch iscompounded into the polyolefin resin, and the resulting mixture ismolded as intact.

According to the invented method for marking a molded article, a surfaceof a molded article obtained from the invented resin composition isirradiated with a laser and is marked.

The molded article can be obtained by conventional molding processes foruse in molding (forming) of plastics, such as extrusion molding (film,sheet, deformed), injection molding, blow molding, and compressionmolding.

The type of lasers for use in marking is not particularly limited andthe laser may be any of, for example, gas lasers, semiconductor lasers,and excimer lasers. Among them, Nd:YAG laser is most advantageouslyused. The technique for marking is not particularly limited, and markingcan be performed by known or conventional techniques. To improve markingprecision, a technique is preferred in which a laser is condensed into aspot having an appropriate size by a conventionally known opticaltechnique, and the resulting laser spot is applied on a surface of themolded article with a scanning apparatus having a combination of aplurality of optical mirrors controlled by a computer so as to form amark having a desired shape. The type of marking is not particularlylimited and may be any of, for example, characters, symbols, graphics,pictures and photographs.

The invented marking method can easily yield a molded article having, ona surface, a mark having a desired shape with a sharp and uniformcontrast.

The invented resin composition capable of laser marking and markingmethod, in which specific components are compounded into a polyolefinresin, can form, with a laser, a mark having a sharp and uniformcontrast on a surface of a molded article.

Additionally, in the invented marked molded article, a mark formed on asurface has a sharp and uniform contrast.

In addition and advantageously, workability and mechanicalcharacteristics of the resin composition and molded article are notdeteriorated.

The present invention will be illustrated in further detail withreference to several examples below, which are not intended to limit thescope of the invention. The following polymers, carbon blacks, metalliccompounds, and dispersing aids were used in examples and comparativeexamples.

[Polymer]p PP: a polypropylene having MI (=MFR) of 10 (g/10 min.) and aflexural modulus of 13000 kgf/cm²

PP/Elastomer: a substance obtained by melting and blending 80 parts byweight of the aforementioned PP and 20 parts by weight of an elastomer[produced by Sumitomo Chemical Co., Ltd. under the trade name of“BONDINE HX8290”] with a conventional extruder

PE/Elastomer: a substance obtained by melting and blending 80 parts byweight of [a product of Mitsui Chemicals, Inc. under the trade name of“HIZEX 1300J”] and 20 parts by weight of an elastomer [produced bySumitomo Chemical Co., Ltd. under the trade name of “BONDINE HX8290”]with a conventional extruder

[Carbon Black (CB)]

CB-1: furnace black (mean particle size: 20 nm)

CB-2: acetylene black (mean particle size: 40 nm)

CB-3: ketjen black (mean particle size: 25 nm)

[Metallic Compound]

M-1: titanium oxide

M-2: zinc oxide

M-3: potassium titanate

[Dispersing Aid]

DA-1: ethylenebisstearamide

DA-2: stearic acid

DA-3: zinc stearate

DA-4: calcium stearate.

EXAMPLES 1 TO 8

Resin compositions capable of marking in white were respectivelyprepared by mixing a polymer, a carbon black (as a laser-susceptiblecomponent), and a dispersing aid in a proportion indicated in Table 1,and a series of molded plate articles having a thickness of 2 mm wereobtained therefrom by injection molding. A surface of each of the moldedarticles was laser marked and a sharp printing could be formed in anycase.

EXAMPLES 9 TO 14

Resin compositions capable of marking in black were respectivelyprepared by mixing a polymer, a metallic compound (as alaser-susceptible component), and a dispersing aid in a proportionindicated in Table 2, and a series of molded plate articles having athickness of 2 mm were obtained therefrom by injection molding. Asurface of each of the molded articles was laser marked and a sharpprinting could be formed in any case.

EXAMPLES 15 TO 17

Resin compositions capable of marking in black were respectivelyprepared by mixing a polymer, a metallic compound and a carbon black (aslaser-susceptible components), and a dispersing aid in a proportionindicated in Table 3, and a series of molded plate articles having athickness of 2 mm were obtained therefrom by injection molding. Asurface of each of the molded articles was laser marked and a sharpprinting could be formed in any case.

Comparative Examples 1 to 6

Resin compositions capable of marking in white were respectivelyprepared by mixing a polymer, a carbon black, and a dispersing aid in aproportion indicated in Table 4, and a series of molded plate articleshaving a thickness of 2 mm were obtained therefrom by injection molding.A surface of each of the molded articles was laser marked and no sharpprinting could be formed in any case.

Comparative Examples 7 to 10

Resin compositions capable of marking in black were respectivelyprepared by mixing a polymer, a metallic compound, and a dispersing aidin a proportion indicated in Table 5, and a series of molded platearticles having a thickness of 2 mm were obtained therefrom by injectionmolding. A surface of each of the molded articles was laser marked andno sharp printing could be formed in any case.

TABLE 1 Polymer Carbon Black Dispersing aid Amount Amount Amount Type ofPrinting Type (wt %) Type (wt %) Type (wt %) Laser Mark Quality Ex. 1 PP99.94 CB-1 0.05 DA-1 0.01 white mark sharp Ex. 2 PP 99.6 CB-1 0.2 DA-10.2 white mark sharp Ex. 3 PP 98.5 CB-1 1 DA-1 0.5 white mark sharp Ex.4 PP 96 CB-1 3 DA-1 1 white mark sharp Ex. 5 PP 98.5 CB-1 1 DA-2 0.5white mark sharp Ex. 6 PP 98 CB-1 1 DA-2 1 white mark sharp Ex. 7 PP98.2 CB-2 1 DA-3 0.8 white mark sharp Ex. 8 PP 98.2 CB-3 1 DA-3 0.8white mark sharp

TABLE 2 Metallic Polymer Compound Dispersing aid Amount Amount AmountType of Printing Type (wt %) Type (wt %) Type (wt %) Laser Mark QualityEx. 9 PP 99.29 M-1 0.7 DA-1 0.01 black mark sharp Ex. 10 PP 98.8 M-1 1DA-1 0.2 black mark sharp Ex. 11 PP 89.5 M-1 10 DA-1 0.5 black marksharp Ex. 12 PP 69 M-1 30 DA-1 1 black mark sharp Ex. 13 PP 89.5 M-2 10DA-1 0.5 black mark sharp Ex. 14 PP 89 M-3 10 DA-1 1 black mark sharp

TABLE 3 Metallic Carbon Dispersing Type Polymer Compound Black aid ofAmount Amount Amount Amount Laser Printing Type (wt %) Type (wt %) Type(wt %) Type (wt %) Mark Quality Ex. PP 88.5 M-1 10 CB-1 1 DA-1 0.5 blacksharp 15 mark Ex. PP/ 88.5 M-1 10 CB-1 1 DA-1 0.5 black sharp 16Elastomer mark Ex. PE/ 88.5 M-1 10 CB-1 1 DA-1 0.5 black sharp 17Elastomer mark

TABLE 4 Polymer Carbon Black Dispersing aid Type of Amount Amount AmountLaser Printing Type (wt %) Type (wt %) Type (wt %) Mark Quality Com. PP99.995 CB-1 0.005 DA-1 0 white illegible Ex. 1 mark with low contrastCom. PP 90 CB-1 10 DA-1 0 white unsharp with Ex. 2 mark poor CBdispersion Com. PP 99 CB-1 0 DA-1 1 white out of Ex. 3 mark printingCom. PP/ 99 CB-2 0 DA-3 1 white out of Ex. 4 Elastomer mark printingCom. PE/ 99 CB-2 1 DA-3 0 white unsharp with Ex. 5 Elastomer mark poorCB dispersion Com. PP 99 CB-3 1 DA-3 0 white unsharp with Ex. 6 markpoor CB dispersion

TABLE 5 Metallic Polymer Compound Dispersing aid Amount Amount AmountType of Printing Type (wt %) Type (wt %) Type (wt %) Laser Mark QualityCom. PP 95 M-1 5 DA-1 0 black unsharp with Ex. 7 mark poor titaniumoxide dispersion Com. PP 99 M-1 0 DA-1 1 black illegible Ex. 8 mark withunsharp printing Com. PP 90 M-1 10 DA-2 0 black unsharp with Ex. 9 markpoor titanium oxide dispersion Com. PP 99 M-1 0 DA-4 1 black illegibleEx. 10 mark with unsharp printing

What is claimed is:
 1. A resin composition for white marking, which iscapable of laser marking and is capable of printing in white with alaser, comprising a polyolefin resin in combination with a carbon blackhaving a mean particle size of 10 to 100 nm and a dispersing aidselected from higher fatty acids and higher fatty acid amides, whereinsaid carbon black and dispersing aid are present, respectively, in anamount of 0.03 to 4% by weight and in an amount of 0.005 to 6% byweight, relative to the weight of the overall resin composition.
 2. Aresin composition for black marking, which is capable of laser markingand is capable of printing in black with a laser, comprising apolyolefin resin in combination with a carbon black having a meanparticle size of 10 to 100 nm, a metallic compound white pigment, and adispersing aid selected from higher fatty acids and higher fatty acidamides, wherein said carbon black, metallic compound white pigment, anddispersing aid are present, respectively, in an amount of 0.03 to 4% byweight, in an amount of 0.2 to 50% by weight, and in an amounts of 0.005to 6% by weight, relative to the weight of the overall resincomposition.
 3. The resin composition for black marking according toclaim 2, wherein said higher fatty acid compounds are higher fatty acidamides.
 4. The resin composition according to any one of claims 1 to 3,wherein said polyolefin resin is a polypropylene.
 5. The resincomposition according to any one of claims 1 to 3, further comprising anelastomer.
 6. The resin composition according to claim 5, whichcomprises 0.5 to 30 parts by weight of the elastomer relative to 100parts by weight of the polyolefin resin.
 7. A method for white markingof a molded article, comprising the step of irradiating a surface of amolded article with a laser to thereby mark the surface in white, saidmolded article being made from a resin composition for white markingaccording to claim
 1. 8. A method for black marking of a molded article,comprising the step of irradiating a surface of a molded article with alaser to thereby mark the surface in black, said molded article beingmade from a resin composition for black marking according to claim 2 or3.
 9. A molded article composed of the resin composition for whitemarking according to claim 1, said article having a surface which ismarked in white with a laser.
 10. A molded article composed of the resincomposition for black marking according to claim 2 or 3, said articlehaving a surface which is marked in black with a laser.